In the field of display, the flexible printed circuit (FPC) and the chip on film (COF) have been widely used for connecting screens and driving circuit boards.
A flexible printed circuit (FPC) is a printed circuit board having high reliability and excellent flexibility, which is produced by using a polyimide or polyester thin film as a base material. The flexible printed circuit has the characteristics of high wiring density, light weight, small thickness, and good bendability. A chip on film or chip on flex (COF) is a chip on film technique fixing a driving integrated circuit (IC) on a flexible wiring board, and is a technique for bonding a chip and a soft substrate circuit by using a soft additional circuit board as a packaging chip carrier. Simply, the difference between them is whether there is a driving IC fixed on FPC.
The mode for connecting a screen glass and a driving circuit board to a flexible printed circuit or a chip on film is a bonding process. In a practical process, an adhesive-type coating (such as an ultraviolet-curable adhesive (UV adhesive), etc.) may be typically added in a bonding zone in order to enhance the strength of connection and prevent the corrosion or short circuit of leads induced by water vapor intrusion.
Although this treatment may achieve the design object thereof to some extent, there is still a relatively large ratio of coating defects after coating an UV adhesive in view of the effect in practical use. This coating defects together with the mechanical damage in a later period and other reasons may result in decrease in mechanical strength. Particularly, there may be a risk of corrosion or short circuit of leads caused by water vapor intrusion. However, it is difficult to detect this risk based on the existing design, thereby resulting in a relatively high market risk of products.